Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle member. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the recording medium as the printhead is moved relative to the medium. The medium is typically shifted each time the printhead has moved across the medium. The thermal inkjet printer is fast and quiet, as only the ink strikes the recording medium. These printers produce high quality printing and can be made both compact and affordable.
In one prior art design, the inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) a metal nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the recording medium.
One prior art print cartridge is disclosed in U.S. Pat. No. 4,500,895 to Buck et al., entitled "Disposable Inkjet Head," issued Feb. 19, 1985 and assigned to the present assignee.
Nozzle members or orifice plates for inkjet printheads often are formed of nickel and are fabricated by lithographic electroforming processes. One example of a suitable lithographic electroforming process is described in U.S. Pat. No. 4,773,971, entitled "Thin Film Mandrel" and issued to Lam et al. on Sep. 27, 1988. In such processes, the orifices in a nozzle member are formed by overplating nickel around dielectric discs.
In a thermal inkjet printer incorporating these types of discrete printheads, the thin film heaters are selectively energized while a mechanism transports the printhead across a recording medium, typically a sheet of paper. The recording medium is incrementally moved perpendicular to the travel path of the printhead so as to enable printing at virtually any location on the recording medium.
To increase the speed of printing per line on a medium and to reduce the mechanical complexity of a printer, it is known to mount separate printheads side by side to form a fixed array of printheads extending across an entire width of a medium. Selected printing elements across the array of discrete printheads are energized simultaneously to print an entire line of dots onto the medium. After the line is printed, the medium is incrementally shifted perpendicular to the array of printheads, and the printing process is repeated.
Drawbacks of this construction of an array of discrete printheads include increased electrical complexity, difficulty in precisely aligning the printheads with one another, and increased cost in providing the plurality of printheads.
As is apparent, with resolutions of inkjet printers becoming greater than 300 dots per inch, alignment of the orifices between discrete inkjet printheads across an array of eight inches or more requires extremely precise positioning to achieve satisfactory spacing between printed dots on a medium. This alignment must be maintained throughout the useful life of the product and under different conditions of duty cycle, temperature, shock, and vibration.
Thus, what is needed is an improved wide printhead structure and a method for fabricating a wide printhead structure, where precise alignment of the orifices across the printhead may be accomplished simply and precisely maintained over the life of the product and over a wide range of operating conditions.